1. Field of the Invention
The present invention relates to a solid-state imaging device, and more particularly, a solid-state imaging device capable of improving characteristics.
2. Description of Related Art
FIG. 4 is a schematic surface view of a CCD solid-state imaging device. This solid-state imaging device 1 includes: a plurality of photoelectric conversion elements (photodiodes: pixels) 2 formed by being arranged in a two-dimensional array in a surface portion of a semiconductor substrate; a vertical charge transfer path (VCCD) 3 formed along each pixel array; a horizontal charge transfer path (HCCD) 4 formed along an end portion in the transferring direction of each vertical charge transfer path; and an amplifier 5 provided at an output end portion of the horizontal charge transfer path 4, for outputting, as an imaging signal, a voltage signal according to the charge amount of a signal charge being transferred.
FIG. 5 is a schematic sectional view of a section along a line V-V of FIG. 4, that is, a pixel part. A photodiode (pixel) is constituted by an n-region 12 (to which the pixel 2 of FIG. 1 corresponds) being formed in a p-well layer 11 of the semiconductor substrate, and on the topmost surface of the n-region 12, a high-density p-layer 13 for dark current suppression is formed.
On both sides of the pixel 2 (n-region 12), formed are n-regions 3a that form buried channels of the vertical charge transfer paths 3, and a high-density p-layer 14 is provided under the n-region 3a. In the illustrated solid-state imaging device, due to a structure where an accumulated charge in the n-region 12 is read out to the vertical charge transfer path 3 on the left side, a high-density p-region 15 to serve as a channel stop is provided between the n-region 12 and the n-region 3a on the right side.
On the buried channel 3a of the vertical charge transfer path 3, a transfer electrode film 3b is formed via an insulating layer. On a light receiving surface of the semiconductor substrate surface portion, a conductive light shielding film 16 such as an aluminum film or a tungsten film is formed. In this light shielding film 16, an opening 16a is provided at a position above each n-region 12. A flattening layer 17 is stacked on the light shielding film 16, and at a position thereon corresponding to each n-region 12, a color filter 18 and a microlens 19 are provided.
Various voltages are applied to the light shielding film 16. For example, a plus voltage is applied when reading out the accumulated charge in n-region 12 to the adjacent buried channel 3a. Moreover, as a result of a minus voltage being applied on occasions other than readout, blooming and smear characteristics are improved.
For thus applying various voltages to the light shielding film 16, in the example shown in FIG. 4, one of the connection pads 20 provided in a peripheral portion of the solid-state imaging device 1 and the light shielding surface 16 are electrically connected by wiring 21, and as a result of a voltage being applied to the connection pad 20 from the outside, applied voltage control of the light shielding film 16 is performed.
Also, documents relating to techniques for applying a predetermined voltage such as a read voltage to a light shielding film include, for example, JP-A-2003-258234 and JP-A-2005-109021.
Miniaturization of recent solid-state imaging devices has advanced together with the increasing number of pixels, and thinning of the wiring 21 shown in FIG. 4 has also advanced. However, when the wiring 21 is thinned, a time constant of the wiring 21 is increased, so that a read pulse to be applied to the light shielding film 16 has a rounded pulse waveform.
In other words, sufficient effects as being a readout gate may not be obtained. Moreover, since the amount of current flowing through the wiring 21 is increased, reliability of an imaging device declines.
Furthermore, it can be considered that a voltage to be applied to the light shielding film 16 having a large area becomes nonuniform in the light shielding film, that is, in a pixel region, and there is a possibility that a read voltage and characteristics of, blooming, smear, and the like vary in a plane.